1. Field of the Invention
The present invention relates to a belt driven tape cartridge for backing up data of, e.g., a computer, in which a magnetic recording tape is driven by a belt.
2. Description of the Related Art
Over the recent years, for backing up data used in a computer, there has been employed a tape cartridge in which a magnetic recording tape is driven by a belt (which cartridge is hereinafter be termed a "belt driven tape cartridge).
A construction and an operation of the belt driven tape cartridge will hereinafter be briefly described. Note that U.S. Pat. No. 3,692,255, U.S. Pat. No. 4,581,189, U.S. Pat. No. 4,262,860 and U.S. Pat. No. 4,466,564 should be referred to for greater details of the belt driven tape cartridge.
A typical belt driven tape cartridge has such a construction that a box body incorporates a pair of tape reel hubs for accommodating a magnetic recording tape, a belt for rotating the tape reel hubs (for running the magnetic recording tape), and belt drive rollers.
Normally, the box body is constructed of a baseplate composed of a metal such as aluminum and an upper half composed of plastic such as polycarbonate. A surface (hereinafter referred to as a front surface) of the upper half, which surface becomes an inserting side when inserted into a recorder, is formed with first and second openings into which a drive roller and a head of the recorder are respectively inserted when set in the recorder.
A belt drive roller is provided in the vicinity of the second opening of the baseplate. More specifically, the belt drive roller is disposed in such a position as to come into contact with the drive roller of the recorder when the belt driven tape cartridge is set in the drive. The pair of tape reel hubs are provided on the baseplate in such a form that the hubs can not be rotated directly from outside of the box body. Further, the baseplate is provided with members for determining a route for the magnetic recording tape so that the magnetic recording tape wound round one tape reel hub passes by in the vicinity of the first opening and reaches the other tape reel hub. Moreover, the baseplate is also provided with members for holding the belt so as to be always kept in pressure-contact with the belt drive roller and with the magnetic recording tape wound both of the tape reel hubs irrespective of quantities of the magnetic recording tape wound round the respective tape reel hubs.
That is, in the belt driven tape cartridge, a force enough to rewind the magnetic recording tape round the periphery of one tape reel hub at the same velocity as a velocity of the belt, is applied to the one tape reel hub. Further, a force enough to wind the magnetic recording tape round the periphery of the other tape reel hub at the same velocity as the belt velocity, is likewise applied to the other tape reel hub. Therefore, the belt driven tape cartridge is capable of abruptly accelerating and decelerating the magnetic recording tape.
The belt driven tape cartridge is used in such a state that a running speed of the magnetic recording tape is about 90 ips in order to utilize the above-described characteristics. In other words, the air is drawn between layers of the magnetic recording tape wound thereon.
When the air is drawn between the layers of the magnetic recording tape, there occurs a phenomenon called a winding deviation (a pack shift), wherein the magnetic recording can not be normally wound round the tape reel hubs. If this pack shift occurs, a relative positional relationship between the head and the magnetic recording tape becomes different every running process, with the result that a good quality record and reproduction can not be carried out.
It is well known that a roughening process on a surface (one or both of a magnetic recording layer and a back coat layer) of the magnetic recording tape is effective to prevent the occurrence of the pack shift. If the surface of the magnetic recording layer is excessively roughened, however, a spacing loss increases, and consequently a C/N deteriorates. Further, in the belt driven tape cartridge, a comparatively large pressure caused by the drive belt is applied to the magnetic recording tape wound round the tape reel hub, and hence, if the surface of the back coat layer is excessively roughened, there appears a phenomenon (known as print-through), wherein a surface configuration on the back coat layer of the magnetic recording tape laminated contiguously on the magnetic recording layer of the magnetic recording tape, is transferred on this magnetic recording layer.
Therefore, the surface of the magnetic recording tape has hitherto been roughened properly so that degrees of deterioration of the C/N, the print-through and the pack shift fall within allowable ranges.
On the other hand, it is required that the surface of the magnetic recording layer be more flattened and the running speed of the magnetic recording tape be made by far faster to obtain the belt driven tape cartridge capable of recording and reproducing the data at a high speed and a high density. When increasing the tape running speed, the air is more easily drawn in between the layers of the magnetic recording tap, and therefore the pack shift is easy to occur. Further, when the magnetic layer is flattened, the air drawn between the layers of the magnetic recording tape tends to remain therebetween, which also makes it easy to cause the pack shift. Under such conditions where the pack shift is easy to occur, the surface property of the magnetic recording tape is required to be controlled more precisely than by the prior arts in order to obtain the belt driven tape cartridge contrived to prevent the occurrence of the pack shift as well as to cause no print-through and to obtain an enhanced C/N.